Process for the removal of oxidizable sulfur compounds from a hydrocarbon gas mixture



Jan. 1, 1952 w. w. oDELL 2,581,135

PROCESS FOR THE REMOVAL OF OXIDIZABLE SULFUR COMPOUNDS FROM AHYDROCARBON GAS MIXTURE Filed Feb. 12, 194s I nvenir g miam@ PatentedJan. 1, 1952 Paocass VFoa 'rim REMOVAL F OXIDIZ- ABLE SULFUR COMPOUNDSFROM A HY- DROCARBON GAS MIXTURE William W. Odell, Elizabeth, N. J.,assignor to Standard Oil Develo ration of Delaware pment Company, a,corpo- Appllcatlon February 12, 1948, Serial No. 7.985

3 Claims.

This invention relates to process of promoting oxidation of combustiblematter.y In particular it relates to the preferential oxidation of oneor more components of a mixture of different oxidizable materials whilein the gaseous or vapor phase. It deals with the oxidation of readilyoxidizable sulphur compounds when the latter are present in a gaseousmixture in such a manner that products of oxidation may readily beremoved from the unoxidized gases. It also relates to the production andrecovery of by-products in the treatment, purification and partialoxidation of combustible matter which matter is initially present in themixture and in the vapor phase.

It has been found to be costly and difllcult to remove hydrogen sulphidefrom natural gas when it is present therein in very appreciable amountssuch as 1000 grains or more per 100 cubic feet. The old procedures usingiron oxide mixed with shavings is cumbersome and requires extremelylarge apparatus and is adaptable for use chiefly at low pressures. It iscustomary so far as is known to use an amino compound or other basicmaterial such as an alkaline phosphate as an absorbent for this sulphurgas by contacting it with the gas usually under pressure andregenerating the solution for recirculation in contact with additionalvolumes of gas. This procedure is costly and the by-products are notrecoverable without further expenditure of effort and materials.However, in this invention the hydrogen sulphide is preferentiallyoxidized under such conditions and in the presence of a particular'amount of an oxidant that it reacts substantially completely withoutappreciable oxidation of other gaseous components associated therewith.Preferential oxidation of a component of a gas mixture is not in itselfnew but the effects obtained in the practice of this invention are newand the conditions under which the reactions are promoted are specificto this case.

One of the major objects of this invention is to oxidize a component ofa gasiform mixture under conditions whereby an appreciable excess ofoxidant is not required and under conditions such that substantiallynone of the other components of the mixture is simultaneously oxidized.Another object' is to so preferentially oxidize a particular componentof a gasiform mixture that a recoverable valuable by-product isproduced. Still another object is to accurately control the temperaturewhile promoting limited oxidation of combustible matter in contact witha catalyst so that optimum yields of desired oxidation products areobtained. Another object of this invention is to promote preferentialoxidation of a gasiform mixture under conditions whereby the effluentstream of reaction products is substantially free of excess oxidant.Other objects will become evident from the disclosures made hereinafter.

Generally, the reactions which occur in the practice of this inventionare exothermic in nature and may be typified by Equations 1 to 5 belowwhich arereactions in which sulphur compounds are oxidized. Althoughthis invention is by no means limited to the oxidationof sulphurcompounds, as will become apparent, the equations are presented becausethey are typical and because they relate to reactions which occur in theexamples.

Calories 1) HzS-|-1/O2=H2O+S +65,'700 (2) H2S+11/O2=H2O+S0z 4436.700 (3)CSZ+3O2=CO2+2SO2 +265,130 (4) Csz+2H2O=CO2|2H2S +128,330 (5)2H2S+SO2=3S+2H2O +60,400

It is well known that hydrogen sulphide oxidizes according to Reactions1 and 2 and it is known that reaction 2 takes place substantially to theexclusion of Reaction 1 when the amount of oxygen present duringoxidation is sufliciently great. It hasy been found difllcult to promotethe reaction shown in Equation l Without some SO2 forming and withoutusing an excess of oxygen. It has further been found diilcult to controlthe reactions when employing fixed beds of refractory or catalystmaterial as contact medium. In fact it appears that practicalapplication of known principles has been retarded because of thesediiiiculties. In the practice of this invention HzS may be oxidizedunder controllable temperature conditions Without employing excessiveamounts of oxidants and reaction can be promoted as indicated byEquation 1 or Equation 2; the conditions for accomplishing this arespecic. The invention can best be described with r'erence to thedrawing.

The drawing shows diagrammatically and largely schematically inelevation one form of apparatus in which this invention may bepracticed.

Referring to the drawing, the reactor i is adaptedto confine a bed offinely divided solids, and in which the solids may be fluidized bygasiform stream. 'I'he solids may be either catalytic or non-catalytic,or a mixture of catalytic and non-catalytic solids, the latter beingparticularly advantageous when the concentration ofv ,3 the more readilyoxidizable -component of the gaseous mixture is appreciable. The reactoris connected to inlet valve 2 for introducing a gael-- form fluid to betreated, to valve 5 for intro- The gasiform stream upon passinglupwardlyv through the reactor leaves through dust collector -2li,ofltake E, valve l, and conduit`\,33, to heat exchanger 23, from whichitpasses throughvalve 24 and conduit 36, to scrubber 3 I, from which itexits through valve 32. Outlet valves for bleeding vthe gas are shownvat 34 and 35.' The middle portion of the reactor is jacketed as shown at8 and confines a temperature controlling medium 9. Finely divided solidswhich solids are commonly catalytic solids are confined in reactor I andwhen these are fiuidized they have a leveldesignated as L in thedrawing. Upon drawingofl' finely dividedsolids which may be donecontinuously they pass through oitake III and valve II, into treatingchamber .I2,` wherein a bed of the solids is maintained with a definitepredetermined level such as is indicated by LT. Coolant is introducedinto the treater I2, in amounts required through valve I3, passingupwardly through grid I-.A and through the mass of solids in the treaterand out through ofitake valve IS.- 'I'he finely divided solids afterbeing temperaturecontrolled.

cooled for'example, are withdrawn. from 'treater I2, usuallycontinuously passing'through offtake I4,.up to reservoir I6, throughvalve 28. 'I'he off gases from I6 are discharged through valve I'I andthe cooled solids collecting in reservoir I6, pass through valve I8,back to reservoir I for recirculation. In'order lthat the solids maybetruly countercurrently contacted with the 'temperature controlled mediumin treater I2, this treater is preferably largely filled with relativelylarge size packing material which material prevents the ebullient motionof the solids throughout the bed in treater I2. Coolant for jacket l,

is supplied through valve 2| and is discharged, commonly in the vaporphase, through valve 22; th'e discharged vapor can, of course, becondensed and recirculated. The raw gas to be treated passes at least inpart through inlet valve 31 to heat exchanger 23'and thence preheatedthrough conduit 2B and valve 21 to conduit 30 and mixing chamber 3 toreactor I. Extra, finely divided solids are supplied to the system asneeded through valve 40 to the reservoir I6. 'Ihe double arrows indicatea supply of a fiuidizing medium in amounts required to maintain thesesolids in a substantially uidized state.

Example 1.-Referring to the drawing the invention will be illustrated bytreating a natural gas containing 2% of hydrogen sulphide and recoveringsulphur therefrom. AThis amount'of sulphur represents approximately 1274grains per 100 cubic feet of gas. used in the particular example arepreferably catalytic to the oxidation of hydrogen sulphide: they maycomprise kaolin, alumina, iron oxide or mixtures of these or they maycomprise other oxidation catalysts known to function catalytically inthis capacity. The size of the solids should preferably be 20 to 150mesh. The' gas supplied to mixing box 3, preferably shold be at atemperature above about 300 C. regardlessl of whether `it is introducedentirely through valve 2. entirely through valve 21, or partly througheach of these valves. The gas entering the 69m' The finely dividedsolids 4 t bustlon zone is preheatedin order` that a great part of thecombustionzone-will not be wasted in bringing the gases up to theignition temperature of the more readily oxldizable component of thegaseous mixture. In this manner' also'uniform temperature is morereadily obtained in the bed in that it will not be lrelatively cool at.

the bottom and relatively hot at the top.` Oxygen or a gas 'containingoxygen but preferably not air because of the dilution effect of thenitrogen is introduced through valve 5 and the amount used isapproximately and very -closely 10 cubic.

feet of oxygen equivalent per -1000 cubic feet of total natural gas tobe treated. The mixture of oxygen and preheated gas is passed directlyinto reactor I, up through grid member .I into the mass of catalyticsolids confined therein at such a velocity that the mass 'is inturbulent motion the particles being substantially in ebullient motionwith a bed vlevel substantially as shown' at L. The superficial velocityunder the describedcondition will vary from about 5 feet per second withthe larger size and denser catalyst particles to less than i foot persecond with the smaller particles and/or less dense catalyst. In thisexample the hydrogen sulphide is oxidized in accordance with Equation land the temperature throughout the bed in reactor I is maintainedsubstantially uniform at approximately 4509 C. 'I'he gas outlettemperature, namely the temperature ofthe gas leaving reactor I throughoitake 6 is approximately 500 C. and the inner surface. of thetemperature controlled portion of the reactor wall is substantially 400C. or

somewhat less. Under these conditions the reaction will proceedsubstantially quantitatively without employing any appreciable excess ofoxidant and the sulphur resulting from reaction will pass out in thevapor phase in the gas stream containing the natural gas, leavingthrough offtake B. It is necessary to supply a coolant through valve 2Ito the reactor jacket in amounts adapted to remove approximately 30.00B. t. u. per 1000 cubiclfeet ofthe natural gas treated. The coolant maybe such a material as diphenyl 5 ether, diphenyl benzene or othercoolant circulated preferably under superatmospheric pressure adapted tomaintain the chosen wall temperature. Catalyst of 20 to 150 m'esh ispreferably employed asdescribed so that the necessary high 0 velocity ofstream flow through thel catalyst bed can be employed without carryingover excess of catalyst; high velocity and resultant low contact timewith the catalyst is desirable to prevent the occurrence of secondaryreactions which will occur if prolonged time of contact is maintained.Such a side reaction is Secondary reactions can not be -avoided in a xedbed of catalyst of any appreciablediameter anddepth because ofoverheatinguof the catalyst and channeling. It is found in' employing aI fixed bed thatran excess of oxygen is required in order to carry outthe reaction and that inevitably an appreciable amount of the sulphur'content of the'gas appears as SO2 in the gas stream containing thereaction products. The depth of bed in reactor lI, that is the depthfrom level L to grid l, is preferably not more than 10 feet and may beappreciably less than 10 feet when the catalyst isiinely divided or osuch density that the velocity of the flow of the reactant stream isvrelatively low. The sulphur passing overhead from reactor I iscondensed in heat exchanger 2l and withdrawn as a liquid through valveIl at a temperature at which moulten sulphur is not highly viscous. Thepreferred duration of contact of the gasiform stream with the tlnelydivided catalyst in reactor I is preferably more than l second and lessthan seconds.

Example 2.-Again-referring to the drawing and employing as a gas to betreated the same kind of gas as in Example 1. In this case theoperations are substantially the same as described in Example l onlythat oxygen is supplied in amounts substantially as indicated byEquation 2, the oiftake gases in this instance comprise, besides theunreacted natural gas components, H2O and SO2 which are passed throughoii'take 6. valve 1. conduit 33 to heat exchanger 23 and valve 35. Aneutralizing agent such as ammonia is introduced into the down streamside of valve 85 by opening valve 4I, whereby the SO: and H2O are causedto react with the NH: forming upon proper cooling the sulphite or acidsulphite according to the amount of NH3 introduced. sulphite formed maybe removed from the gas stream as a solid by known means and oxidized tosulphate in this form very readily when desired. Equations whichrepresent these reactions are:

More heat is generated in this case than in Example i and it isaccordingly necessary that suiilcient cooling be provided in reactor Iso that the temperature will not rise to such a point that the otherconstituents of the natural gas will be oxidized. Apparently it isnotpossible to accomplish this employing a xed bed of catalyst withoutsimultaneously burning some of the hydrocarbons of the natural gas. Evenwith a iluidized bed of solids it is essential that the temperature inthe bed in reactor I be kept below approximately 450 C. in order toavoid hydrocarbon oxidation.

It will be noted that in the foregoing two examples the hydrogensulphide content of the gas treated was initially 2%. When largeramounts of hydrogen sulphide are present in the gas treated appreciablymore heat is generated in the reactor and therefore, more heat must beremoved from the reactor per unit of time other factors remaining thesame, than when lesser amounts of HnS are oxidized. It is helpful intreating gases with large amounts of oxidizable material and generatinglarge amounts of heat in reactor I, to circulate solids from the reactorto a treater wherein they are cooled and then return the cooled solidsto the upper portion of the reactor as a heat absorbing medium as wellas catalyst. 'Ihe solids from reactor I are circulated through conduit I0 and valve II to the treater I2 and are removed cooled from I2 throughofftake Il and pass upwardly through valve 28 to reservoir I6 from whichthey pass downwardly and they pass through valve I8 under control toreactor I. It will be noted that the cooled solids thus supplied to thereactor mix immediately with the other solids therein because a state ofebullient motion is maintained throughout the bed in reactor I. However,in trea-ter 2 quite the opposite condition is maintained in order thatthe coolant introduced through I3 into treater I2 can be eilectivelyused by countercurrent contact with the solids therein; the treater ispacked with relatively large sire solids having interstices ofsuiiicient size so that the catalyst particles can pass downwardlytherethrough while the gases pass upwardly therethrough. In this mannercooling is provided in reactor I by supplying a large cooling surfacewhich the iluidized particles contact. Cooling is also effected bysupplying cooled catalyst to the turbulent bed lin reactor I at apredetermined rate dependent upon the cooling effect desired.

Because it is possible to so accurately regulate temperature throughouta large mass of catalyst solids in promoting oxidation reactions it ispossible to obtain oxidation effects and selective oxidation moreeillciently than has been attained heretofore so far as is known.

It has been found that by a Ycombination of steps not foreseeable fromthe prior art these unusual results have been obtained. These steps are(1) maintaining a high velocity of ow of gas stream initially containingthe reactants, (2) thorough mixing of the oxidant and the reactantsprior to introduction into contact with the hot solids, (3) employingrelatively coarse grain catalysts which are not too highly active, (4)applying cooling medium to a surfacein contact methane.

with the combustion zone, (5) supplying the gasoxidant mixture to themass at a suitable elevated temperature, and (6) recirculating cooledcatalysts downwardly into the iluidized mass of hot catalystcountercurrently to the upper ow of hot gases.

The operations may be carried out in the preferential oxidation of acomponent of a mixture which is more readily oxidized catalytically thanthe other components of the mixture. Alcohols. aldehydes, and otheroxidation products can be made very eil'ectively when the higherhydrocarbons are oxidized preferentially in the presence of hydrocarbonsof low molecular weight such as Again, organic sulphur compounds such ascarbon bisulphide may be removed from combustible gas by preferentialoxidation at relatively low temperatures.

So far the oxidant has been referred to as oxygen or the oxygen in anoxygen-bearing gas but it will become obvious that other oxidizingagents may be used to promote particular selected ei'- fects. Chlorine,nitric oxide or other gasii'orm oxidant may be employed within the scopeof this invention. Furthermore the procedures described may be conductedat substantially atmospheric pressure or at pressures greatly in excessof atmospheric pressure.

By the term ignition temperature as employed in the appended claims ismeant the temperature at which incipient combustion of the substance canbe promoted under conditions prevailing in contact with the iluidizedsolids.

Having described the invention in a manner so that it may be practicedby those skilled in the art,

What is claimed is:

l. A process for the removal of at least one impurity selected from thegroup consisting of hydrogen sulfide and organic sulfur compound from ahydrocarbon gas mixture containing the same which comprises maintaininga deep bed of turbulent inely-divided iluidized solids which do notchemically react with the impurity in a combustion zone. maintainingsaid solids at a temperature above 300 C. but below 450 C., preheatingthe hydrocarbon gas mixture to a temperature of about 300 C., passingthe preheated gaseous mixture mixed with an amount of oxygen-containinggas substantially chemically equivalent to the amount of impuritypres-4. 'ont in the hydrocarbon gas upwardly through' said bed of hotsolidsv in the combustion zone at a velocity of 1 to 5 ft./sec. adaptedto maintain said solids in said fluidized state in the combustion zoneand thereby promoting the controlled oxidation of the impurity to sulfurvapor without substantially oxidizing the hydrocarbon components of thegas, withdrawing a stream of the hot iiuidized solids at a point nearthe bottom of said combustion zone while simultaneously introducing astream ofthe same cooled solids into the combustion zone at a point nearthe top' thereof at such 'a rate that the temperature of -the udzedsolids is held within the limits of 300 C. to 450 C. and withdrawingfrom the combustion zone above said bed a gaseous stream of hydrocarbonscontaining vaporized sulfur but substantially depleted of said impurity.

the hydrocarbon gas is natural gas.

3. A process according to claim 1 in which the fiuidized bed containstwo solids one of which 20 2. A method according to claim 1 in whichtained in the hydrocarbon gas and one of which is non-catalytic to saidoxidation.

' WZILLLAMW.ODELL.'y

REFERENCES CITED' AThe. following references are of record in the tileof this patent: l

UNITED STATES PATENTS Number Name Date 1,807,528 Hiatt A May 26, 1931l1,922,872 Thompson Aug. 15, 1933 2,298,641 Schulze et al.- Oct. 13, 1942gg 2,340,878 Holt et al. Feb. 8, 1944 2,441,311 Crowley et al. May 11,1948 2,447,043 Weity et al. Aug.17, 1948 FOREIGN PATENTS Number CountryvDate 406,495 Great Britain Mar. 1, `1934 OTHER REFERENCES v Y Chem.MetaliurgicalEng., June 1944; pages 97 and 98.

1. A PROCESS FOR THE REMOVAL OF AT LEAST ONE IMPURITY SELECTED FROM THEGROUP CONSISTING OF HYDROGEN SULFIDE AND ORGANIC SULFUR COMPOUND FROM AHYDROCARBON GAS MIXTURE CONTAINING THE SAME WHICH COMPRISES MAINTAININGA DEEP BED OF TURBULENT FINELY-DIVIDED FLUIDIZED SOLIDS WHICH DO NOTCHEMICALLY REACT WITH THE IMPURITY IN A COMBUSTION ZONE, MAINTAININGSAID SOLIDS AT A TEMPERATURE ABOVE 300* C. BUT BELOW 450* C., PREHEATINGTHE HYDROCARBON GAS MIXTURE TO A TEMPERATURE OF ABOUT 300* C., PASSINGTHE PREHEATED GASEOUS MIXTURE MIXED WITH AN AMOUNT OF OXYGEN-CONTAININGGAS SUBSTANTIALLY CHEMICALLY EQUIVALENT TO THE AMOUNT OF IMPURITYPRESENT IN THE HYDROCARBON GAS UPWARDLY THROUGH SAID BED OF HOT SOLIDSIN THE COMBUSTION ZONE AT A VELOCITY OF 1 TO 5 FT./SEC. ADAPTED TO MAIN-